With its turquoise-striped walls, the industrial complex squatting on bluffs above the Pacific Ocean here looks like a routine factory for high-tech electronics.

But the Rokkasho Nuclear Fuel Facility is instead one of the world’s newest, largest and most controversial production plants for plutonium, a nuclear explosive.

The factory’s private owners said three months ago that it would be ready to open in October as part of a government-sponsored effort to create special fuel for the country’s future nuclear power plants.

Japan’s leaders affirmed last month they intend to proceed with that effort, a decision that has stoked anxiety in East Asia and alarmed U.S. experts _ including some in the Obama administration _ trying to limit the spread of nuclear weapons and keep the explosives out of terrorist hands.

The plant will produce thousands of gallon-sized steel canisters of plutonium, which Japan’s conservative government says will one day be burned in commercial reactors. But in theory, they could fuel a huge nuclear arsenal. In the meantime, U.S. officials worry they may be vulnerable to theft.

Since President Barack Obama’s first term, his administration has lobbied furiously to persuade Japan to take much tougher security measures to protect Rokkasho and other sites against terror attacks.

But so far, Japan has refused to replace the white-gloved, unarmed guards and small police unit stationed here with more formidable forces. Neither has the United States convinced Japan to undertake stringent background checks for Rokkasho’s 2,400 workers, or to conduct more realistic security drills.

After years of U.S. pressure, Japan has quietly agreed to return 730 pounds of high-grade plutonium – perfect for building weapons – to the United States from a site south of Rokkasho. The West supplied the plutonium to Japan’s research reactors during the Cold War.

The deal will be announced this month at a Netherlands summit to promote steps to keep nuclear explosive materials out of terrorists’ hands. But the cache Japan will pledge to return is less than 1 percent of the country’s plutonium hoard, which it has spent decades accumulating.

U.S. officials and experts say Japan has not worked closely enough with its allies on nuclear security, that its agencies have deferred to local and utility officials on safety and security measures, and that it has struggled to come to grips with the scale of the terror threat.

Some Japanese officials argue, meanwhile, that the peaceful nature of their society makes nuclear conspiracies improbable. They say their country can never accept armed guards and background checks because of deeply held cultural objections.

These convictions make U.S. officials nervous. “It is a system that relies heavily on the expectation that everyone will do what they are expected to do,” said a senior Obama administration official, who spoke on condition of anonymity because of the sensitivity of diplomatic discussions on this issue. As a result, he said, “the stuff we would kind of expect to see” at a dangerous nuclear facility “is not there.”

Some prominent Japanese officials agree. Naoto Kan, Japan’s prime minister during the Fukushima disaster in 2011, said in an interview with the Center for Public Integrity that before that crisis safety officials told him they were not concerned about the terror threat.

“‘America might be under terrorist attacks, but Japan is very unlikely to be so,’” they said, according to Kan. “Japan simply didn’t consider terrorism a possibility here. And you may ask whether Japan is prepared for such threats” today, he said. “Well, the answer is that it isn’t prepared for such attacks.”

A consortium of electric utilities, Japan Nuclear Fuels Limited, has spent 22 years building Rokkasho, the cornerstone of a plan to build the world’s first electrical system based on plutonium-powered reactors. Japanese consumers are paying Rokkasho’s $22 billion construction tab through a surcharge on their electric bills.

But by the government’s own account, its first commercial plutonium reactor is decades away from operation. Even if Japan needed plutonium, it already has 9.3 metric tons stored at Rokkasho and nine other domestic sites, along with 35 tons in France and the United Kingdom.

Altogether, Japan’s 44-ton hoard represents about 9 percent of the total world’s supply. After Rokkasho opens, this stockpile could double in just five and a half years. A lump weighing a bit more than 6 pounds – which could easily fit into a thermos _ is enough to make a bomb.

Japan’s approach contrasts sharply with measures adopted by the U.S. Nuclear Regulatory Commission after the 9/11 terror attacks. The new rules led to a 60 percent growth in security forces at U.S. plants, among other things. Washington pressed other nations to take a similar get-tough approach. But the Japanese saw little urgency, current and former U.S. officials say.

Former U.S. diplomat Kevin Maher, who served as a high-ranking official in the Tokyo embassy in the early 2000s, said he and Frances Townsend, then homeland security adviser, met with a senior official at Japan’s Nuclear and Industrial Safety Agency in 2005. “We told him, ‘Your nuclear power plants are very good targets’” for terrorists and that security needed to be tightened, Maher said, adding that he couldn’t recall the official’s name.

“There is no threat from terrorists because guns are illegal in Japan,” the official said, according to Maher. Townsend confirmed the account.

John Thomas Schieffer, U.S. ambassador to Japan from 2005 to 2009, said “the Japanese had a hard time in the beginning conceptualizing that somebody would want to do something in Japan that would result in a loss of life.”

Japan is no stranger to terror, however. Japanese Red Army hijackers commandeered Japanese airliners in the 1970s. Militants with Japan’s Middle Core Faction scorched the ruling Liberal Democratic Party headquarters with a flamethrower in 1984 and launched homemade missiles against the Imperial Palace in 1997.

The gnomic guru of Japan’s Aum Shinrikyo doomsday cult, Shoko Asahara, was obsessed with acquiring an atomic weapon and sought to buy them in Russia after the Soviet Union collapsed. Only after those schemes failed did Asahara turn to chemical weapons, ordering a deadly sarin nerve gas attack that killed 13 on the Tokyo subway system in 1995.

Terrorist Khalid Sheikh Mohammed, captured in May 2003, told interrogators that he had tried to organize the hijacking of a plane at Japan’s Narita airport, with the aim of crashing it into Tokyo’s U.S. Embassy.

In December, Prime Minister Shinzo Abe forced through a new national security law that should allow a freer exchange of threat data with Washington. But that hasn’t quelled U.S. concerns.

“Do they have the weapons and defensive systems that we have at nuclear facilities? Almost certainly not,” the senior administration official said. “History so far hasn’t proven them wrong. But you have to ask, what level of risk are you willing to accept?”

During a recent tour of the Rokkasho plant, an elderly guard in a blue uniform and white gloves bowed as he checked the passports of special guests. Inside the huge complex, a blue van sat near the plant’s small police post.

None of the private security guards is armed. If Rokkasho’s modest forces face overwhelming odds, officials say, they are trained to withdraw and call for help, a routine that U.S. officials have said they find alarming.

The plant relies heavily on electronics for security, including intrusion sensors, computerized authorization lists and biometric identification systems. But breaches still occur. On Aug. 7, 2009, construction workers were accidentally admitted to a secure storage area for lethal high-level wastes, a lapse an internal report blamed partly on distracting “chatter” among guards.

After the tour, Kaoru Yoshida, director of media relations for Rokkasho, made the assertion to the Center for Public Integrity that there was a “100 percent guarantee” that workers at the plant would not steal plutonium, even though they have not been subjected to rigorous background checks.

Ensuring that no undetected theft of plutonium occurs at Rokkasho is technically the responsibility of the International Atomic Energy Agency. When construction started in the late 1980s, the agency’s ambition was to track all but a few kilograms during its production. In practice, this turned out to be impossible.

Processing plutonium requires chopping up spent fuel, dissolving it in acid, separating the plutonium and drying it into a powder. Bits can get stuck in crevices, coat pipes and smear steel walls.

Experts say the IAEA system can account for 99 percent of the plant’s plutonium. But the plant will make 8 metric tons a year. One percent of that is 80 kilograms – enough for 26 bombs, which critics say could leak without detection.

A spokeswoman for the IAEA, Gill Tudor, did not dispute the 99 percent figure, but she expressed confidence that nonetheless “all nuclear material (will remain) . . . in peaceful purposes at the Rokkasho plant.”

Toshihiro Okuyama and Yumi Nakayama, staff writers for the Japanese newspaper Asahi Shimbun, contributed reporting for this article.